Is there any way to make a background image span the entire width of the website instead of having the three separate columns?
Not sure exactly what you're trying to ask; are you asking how to make the bg wider, that makes it span past a 3 column panel layout?
Is your image repeating left-to-right?
All I could think of is making your background image's resolution wider than the span of your layout. I don't believe you have control over how big or small the image appears through theme editing.